Search Results (125)

This study examined the effect of build orientation on the surface finish of micro-optofludic (MoF) devices fabricated via a polydimethylsiloxane (PDMS)-based 3D-printing primary–secondary fabrication protocol, where an inkjet 3D-printing technique was implemented. The molds (i.e., primaries) for fabricating the MoF devices were 3D-printed in two orientations: along $XY$ (Dev-1) and across $YX$ (Dev-2) the printhead direction. Next, the surface finish was characterized using a profilometer to acquire the primary profile of the surface along the microchannel’s edge. The results indicated that the build orientation had a strong influence on the latter, since Dev-1 displayed a tall and narrow Gaussian distribution for a channel width of 398.43 ± 0.29 µm; Dev-2 presented a slightly lower value of 393.74 ± 1.67 µm, characterized by a flat and broader distribution, highlighting greater variability due to more disruptive, orthogonally oriented, and striated patterns. These results were also confirmed by hydrodynamically testing the two MoF devices with an air–water slug flow process. A large experimental study was conducted by analyzing the mean period trend in the slug flow with respect to the imposed flow rate and build orientation. Dev-1 showed greater sensitivity to flow rate changes, attributed to its smoother, more consistent microchannel geometry. The slightly narrower average channel width in Dev-2 contributed to increased flow velocity at the expense of having worse discrimination capability at different flow rates. This study is relevant for optimizing 3D-printing strategies for the fabrication of high-performance microfluidic devices, where precise flow control is essential for applications in biomedical engineering, chemical processing, and lab-on-a-chip systems. These findings highlight the effect of microchannel morphology in tuning a system’s sensitivity to flow rate modulation. Full article

Microfluidic devices are used in numerous scientific fields and research areas, but device fabrication is still a time- and resource-intensive process largely confined to the cleanroom or a similarly well-equipped laboratory. This paper presents a method to create microfluidic devices in under three hours using the silicone polymer polydimethylsiloxane (PDMS) and a laser cut positive master using PDMS double casting without a cleanroom or other large capital equipment. This method can be utilized by an undergraduate student with minimal training in a laboratory with a modest budget. This paper presents “Same Day Microfluidics” as a fabrication method accessible to research groups not currently fabricating their own microfluidic devices and as an option for established research groups to more quickly create prototype devices. The method is described in detail with timing, materials, and technical considerations for each step and demonstrated in the context of a Y-channel coflow device. Full article

Concentration gradient generation plays a pivotal role in advancing applications across drug screening, chemical synthesis, and biomolecular studies, yet conventional methods remain constrained by labor-intensive workflows, limited throughput, and inflexible gradient control. This study presents a novel multilayer microfluidic chip leveraging shear flow-driven partitioning–recombination mechanisms to enable the flexible and high-throughput generation of concentration gradient droplets. The chip integrates interactive upper and lower polydimethylsiloxane (PDMS) layers, where sequential fluid distribution and recombination are achieved through circular and radial channels while shear forces from the oil phase induce droplet formation. Numerical simulations validated the dynamic pressure-driven concentration gradient formation, demonstrating linear gradient profiles across multiple outlets under varied flow conditions. The experimental results revealed that the shear flow mode significantly enhances mixing uniformity and droplet generation efficiency compared to continuous flow operations, attributed to intensified interfacial interactions within contraction–expansion serpentine channels. By modulating hydrodynamic parameters such as aqueous- and oil-phase flow rates, this system achieved tunable gradient slopes and droplet sizes, underscoring the intrinsic relationship between flow dynamics and gradient formation. The proposed device eliminates reliance on complex channel networks, offering a compact and scalable platform for parallelized gradient generation. This work provides a robust framework for optimizing microfluidic-based concentration gradient systems, with broad implications for high-throughput screening, combinatorial chemistry, and precision biomolecular assays. Full article

The Polydimethylsiloxane (PDMS) SlipChip is a microfluidic platform enabling fluid manipulation without pumps or valves, simplifying operation and reducing reagent use. High-viscosity silicone oils (e.g., 5000–10,000 cSt) improve sealing but frequently block microfluidic channels, reducing usability. In contrast, low-viscosity oils (50–100 cSt) reduce blockages but may compromise sealing. This study addresses these challenges by optimizing the viscosity of silicone oil and the curing conditions of PDMS. Low-viscosity silicone oil (50 cSt) was identified as optimal, ensuring smooth slipping and reliable sealing without blockages. Curing conditions were also adjusted to balance adhesion and stiffness as follows: lower temperatures (50–60 °C) enhanced van der Waals adhesion, while higher temperatures (80 °C) increased stiffness. A mixed curing approach (80 °C for the top layer and 60 °C for the bottom layer) further improved performance. Biocompatibility testing using human osteosarcoma cells demonstrated minimal cytotoxicity with 50 cSt oil, supporting cell viability (95%) comparable to traditional multiwell plates. These findings provide practical guidelines for fabricating reliable and biocompatible SlipChips. Full article

In-vitro spermatogenesis holds great potential in addressing male infertility, yet one of the main challenges is separating round spermatids from other germ cells in spermatogonial stem cell cultures. STA-PUT, a method based on velocity sedimentation, has been extensively tested for this application. Though somewhat effective, it requires bulky, expensive equipment and significant time. In contrast, the method of inertial microfluidics offers a compact, cost-effective, and faster alternative. In this study, we designed, fabricated, and tested a microfluidic spiral channel for isolating round spermatids and purifying spermatogenic cells. A commercially available spiral device close to the calculated specifications was tested for rapid prototyping, achieving 79% purity for non-spermatid cells in a single pass, with ability to achieve higher purity through repeated passes. However, the commercial device’s narrow outlets caused clogging, prompting the fabrication of a custom polydimethylsiloxane device matching the calculated specifications. This custom device demonstrated significant improvements, achieving 86% purity in a single pass compared to STA-PUT’s 38%, and that without any clogging issues. Further purification could be attained by repeated passes, as shown in earlier studies. This work underscores the efficacy of inertial microfluidics for efficient, high-purity cell separation, with the potential to revolutionize workflows in in-vitro spermatogenesis research. Full article

Accurate separation in microfluidic devices is crucial for biomedical applications; however, enhancing their performance remains challenging due to computational and experimental constraints. This study aims to optimize microfluidic devices by systematically refining spiral microchannel configurations for the segregation of circulating tumor cells (CTCs) and red blood cells (RBCs) through detailed variable analysis and resource-efficient techniques. The spiral design was developed into six variations, considering loop numbers (2, 3, and 4), aspect ratios (2.333, 3.333, and 5), spiral radii (5, 6, and 7 mm), flow rates (1.5, 2, and 3 mL/min), surface roughness levels (0, 0.5, and 1 μm), and particle sizes (12, 18, and 24 μm). Simulations were conducted in COMSOL Multiphysics and evaluated using the Taguchi method to determine the optimal configuration, reducing the analysis set from 216 to 27 through an efficient experimental design approach. The results identified the optimal structure as having an aspect ratio of 3.333, four loops, a spiral radius of 6–7 mm, a flow rate of 3 mL/min, a surface roughness of 1 μm, and a particle diameter of 24 μm. Among the evaluated parameters, aspect ratio (61.2%) had the most significant impact, followed by the number of loops (13.9%) and flow rate (9.4%). The optimized design demonstrated high separation efficiency and purity, achieving 97.5% and 97.6%, respectively. The fabrication process involved 3D-printing the channel mold, followed by polydimethylsiloxane (PDMS) casting, validating the durability and scalability of the proposed design. This study integrates simulation and experimental results, providing a robust framework for developing next-generation microfluidic devices and advancing diagnostic and targeted therapeutic applications. Full article

Proteins can act as suitable biomarkers for the prognosis and diagnosis of certain conditions and can help us gain an understanding of the fundamental processes that occur inside an organism. In this work, we present a fully automated machine learning-assisted label-free method for the electrical detection of proteins in an integrated microfluidic chip using multi-frequency impedance cytometry and off-the-shelf components for realizing an automated and programmable fluid control system. We verify the robustness of our mixing method on our custom microfluidic mixer composed of polydimethylsiloxane (PDMS) serpentine channels optically using a fluorescent sandwich immunoassay and comparing the results with a commercial benchtop mixer. Salivary IL-6 is a biomarker for oral squamous cell carcinoma (OSCC), and we have demonstrated that our system can be used for the detection of quantification of Interleukin-6 (IL-6) levels in a solution using the impedance response of beads conjugated with the protein of interest, which passes through the microfluidic chip with reasonable accuracy (96%). Although we have demonstrated the detection and quantification of IL-6, our system can be adapted to any protein of interest with slight modification in the reagents and bead-binding protocols. Full article

Recent advancements in microfluidic technologies have revolutionized their applications, particularly in drug monitoring, continuous biochemical analysis, and real-time physiological assessments. However, the fabrication of microfluidic devices with precise flow control remains constrained by either cost-prohibitive photolithography processes or limited-precision 3D printing techniques. In this study, we propose a one-step fabrication method employing picosecond laser processing to directly create microfluidic channels in (PDMS). This method achieves micron-scale channel precision while significantly simplifying the fabrication process and reducing costs. This approach eliminates the need for additional encapsulation steps, further reducing contamination risks and improving production scalability. These findings highlight the potential of this fabrication method to advance next-generation wearable biochemical devices and personalized healthcare technologies. Full article

On-chip microfluidics are advanced in vitro models that simulate lung tissue’s native 3D environment more closely than static 2D models to investigate the complex lung architecture and multifactorial processes that lead to pulmonary disease. Current microfluidic systems can be restrictive in the quantities of biological sample that can be retrieved from a single micro-channel, such as RNA, protein, and supernatant. Here, we describe a newly developed large-scale airway-on-chip model that employs a surface area for a cell culture wider than that in currently available systems. This enables the collection of samples comparable in volume to traditional cell culture systems, making the device applicable to any workflow utilizing these static systems (RNA isolation, ELISA, etc.). With our construction method, this larger culture area allows for easier handling, the potential for a wide range of exposures, as well as the collection of low-quantity samples (e.g., volatiles or mitochondrial RNA). The model consists of two large polydimethylsiloxane (PDMS) cell culture chambers under an independent flow of medium or air, separated by a semi-permeable polyethylene (PET) cell culture membrane (23 μm thick, 0.4 μm pore size). Each chamber carries a 5 × 18 mm, 90 mm² (92 mm² with tapered chamber inlets) surface area that can contain up to 1–2 × 10⁴ adherent structural lung cells and can be utilized for close contact co-culture studies of different lung cell types, including airway epithelial cells, fibroblasts, smooth muscle cells, and endothelial cells. The parallel bi-chambered design of the chip allows for epithelial cells to be cultured at the air–liquid interface (ALI) and differentiation into a dense, multi-layered, pseudostratified epithelium under biological flow rates. This millifluidic airway-on-chip advances the field by providing a readily reproducible, easily adjustable, and cost-effective large-scale fluidic 3D airway cell culture platform. Full article

The propagation of interface acoustic waves (IAWs) in 128° YX-LiNbO₃/SU-8/overcoat structures was theoretically studied and experimentally investigated for different types of overcoat materials and thicknesses of the SU-8 adhesive layer. Three-dimensional finite element method analysis was performed using Comsol Multiphysics software to design an optimized multilayer configuration able to achieve an efficient guiding effect of the IAW at the LiNbO₃/overcoat interface. Numerical analysis results showed the following: (i) an overcoat faster than the piezoelectric half-space ensures that the wave propagation is confined mainly close to the surface of the LiNbO₃, although with minimal scattering in the overcoat; (ii) the presence of the SU-8, in addition to performing the essential function of an adhesive layer, can also promote the trapping of the acoustic energy toward the surface of the piezoelectric substrate; and (iii) the electromechanical coupling efficiency of the IAW is very close to that of the surface acoustic wave (SAW) along the bare LiNbO₃ half-space. The numerical predictions were experimentally assessed for some SU-8 layer thicknesses and overcoat material types. The propagation of the IAWs was experimentally measured in LiNbO₃/SU-8/fused silica, LiNbO₃/SU-8/(001)Si, and LiNbO₃/SU-8/c-Al₂O₃ structures for an SU-8 layer about 15 µm thick; the velocities of the IAWs were found in good agreement with the theoretically calculated values. Although the interest in IAWs was born many years ago for packageless applications, it can currently be renewed if thought for applications in microfluidics. Indeed, the IAWs may represent a valid alternative to standing SAWs, which are strongly attenuated when travelling beneath the walls of polydimethylsiloxane (PDMS) microfluidic channels for continuous flow particle manipulation, provided that the channel is excavated into the overcoating. Full article

Two-layer microfluidic devices with porous membranes have been widely used in bioapplications such as microphysiological systems (MPS). Porous electrodes, instead of membranes, have recently been incorporated into devices for electrochemical cell analysis. Generally, microfluidic channels are prepared using soft lithography and assembled into two-layer microfluidic devices. In addition to soft lithography, three-dimensional (3D) printing has been widely used for the direct fabrication of microfluidic devices because of its high flexibility. However, this technique has not yet been applied to the fabrication of two-layer microfluidic devices with porous electrodes. This paper proposes a novel fabrication process for this type of device. In brief, Pluronic F-127 ink was three-dimensionally printed in the form of sacrificial layers. A porous Au electrode, fabricated by sputtering Au on track-etched polyethylene terephthalate membranes, was placed between the top and bottom sacrificial layers. After covering with polydimethylsiloxane, the sacrificial layers were removed by flushing with a cold solution. To the best of our knowledge, this is the first report on the sacrificial approach-based fabrication of two-layer microfluidic devices with a porous electrode. Furthermore, the device was used for electrochemical assays of serotonin and could successfully measure concentrations up to 5 µM. In the future, this device can be used for MPS applications. Full article

To improve our understanding of Bacillus subtilis growth and biofilm formation under different environmental conditions, two versions of a microfluidic reactor with two channels separated by a polydimethylsiloxane (PDMS) membrane were developed. The gas phase was introduced into the channel above the membrane, and oxygen transfer from the gas phase through the membrane was assessed by measuring the dissolved oxygen concentration in the liquid phase using a miniaturized optical sensor and oxygen-sensitive nanoparticles. B. subtilis biofilm formation was monitored in the growth channels of the microbioreactors, which were designed in two shapes: one with circular extensions and one without. The volumes of these microbioreactors were (17 ± 4) μL for the reactors without extensions and (28 ± 4) μL for those with extensions. The effect of microbioreactor geometry and aeration on B. subtilis biofilm growth was evaluated by digital image analysis. In both microbioreactor geometries, stable B. subtilis biofilm formation was achieved after 72 h of incubation at a growth medium flow rate of 1 μL/min. The amount of oxygen significantly influenced biofilm formation. When the culture was cultivated with a continuous air supply, biofilm surface coverage and biomass concentration were higher than in cultivations without aeration or with a 100% oxygen supply. The channel geometry with circular extensions did not lead to a higher total biomass in the microbioreactor compared to the geometry without extensions. Full article

The capability to record data in passive, image-based wearable sensors can simplify data readouts and eliminate the requirement for the integration of electronic components on the skin. Here, we developed a skin-strain-actuated microfluidic pump (SAMP) that utilizes asymmetric aspect ratio channels for the recording of human activity in the fluidic domain. An analytical model describing the SAMP’s operation mechanism as a wearable microfluidic device was established. Fabrication of the SAMP was achieved using soft lithography from polydimethylsiloxane (PDMS). Benchtop experimental results and theoretical predictions were shown to be in good agreement. The SAMP was mounted on human skin and experiments conducted on volunteer subjects demonstrated the SAMP’s capability to record human activity for hundreds of cycles in the fluidic domain through the observation of a stable liquid meniscus. Proof-of-concept experiments further revealed that the SAMP could quantify a single wrist activity repetition or distinguish between three different shoulder activities. Full article

A microfluidic sweat monitoring patch that collects human sweat for a long time is designed to achieve the effect of detecting the rise and fall of human sweat glucose over a long period of time by increasing the use time of a single patch. Five collection pools, four serpentine channels, and two different valves are provided. Among them, the three-dimensional valve has a large burst pressure as a balance between the internal and external air pressures of the patch. The bursting pressure of the two-dimensional diverter valve is smaller than that of the three-dimensional gas valve, and its role is to control the flow direction of the liquid. Through plasma hydrophilic treatment of different durations, the optimal hydrophilic duration is obtained. The embedded chromogenic disc detects the sweat glucose value at two adjacent time intervals and compares the information of the human body to increase or reduce glucose. The patch has good flexibility and can fit well with human skin, and because polydimethylsiloxane (PDMS) has good light transmission, it reduces the measurement error caused by the color-taking process and makes the detection results more accurate. Full article

Organ-on-a-chip (OOC) is an emerging technology that simulates an artificial organ within a microfluidic cell culture chip. Current cell biology research focuses on in vitro cell cultures due to various limitations of in vivo testing. Unfortunately, in-vitro cell culturing fails to provide an accurate microenvironment, and in vivo cell culturing is expensive and has historically been a source of ethical controversy. OOC aims to overcome these shortcomings and provide the best of both in vivo and in vitro cell culture research. The critical component of the OOC design is utilizing microfluidics to ensure a stable concentration gradient, dynamic mechanical stress modeling, and accurate reconstruction of a cellular microenvironment. OOC also has the advantage of complete observation and control of the system, which is impossible to recreate in in-vivo research. Multiple throughputs, channels, membranes, and chambers are constructed in a polydimethylsiloxane (PDMS) array to simulate various organs on a chip. Various experiments can be performed utilizing OOC technology, including drug delivery research and toxicology. Current technological expansions involve multiple organ microenvironments on a single chip, allowing for studying inter-tissue interactions. Other developments in the OOC technology include finding a more suitable material as a replacement for PDMS and minimizing artefactual error and non-translatable differences. Full article